Page 239 - Design of Reinforced Masonry Structures

4.102 CHAPTER FOUR

P P
Bearing plate Bearing plate

Wall thickness = b Wall thickness = b
h h

L L
(a) (b)
FIGURE 4.28 (a) A wall beam (or deep wall beam or deep beam, supported on
discrete supports at the ends), (b) conventional wall (continuously supported at the
bottom along its entire length).

1. Clear span equal to or less than four times the overall member depth, or
n
2. Regions with concentrated loads within twice the member depth from the face of the
support.”

ACI 318-05 (Section 10.7, Ref. 4.2) also requires deep beams to be designed either
taking into account nonlinear distribution of strain or as suggested in App. A (of ACI 318-
05), which describes a strut-and-tie model. A discussion on the behavior of deep concrete
flexural members can be found in the literature [4.19–4.22].

4.14.3 Examples on Deep Wall Beams
The following examples illustrate the design approach discussed in the preceding section.
*
These examples , originally based on the allowable stress design (ASD) philosophy as
presented in Ref. 4.18 (published in 1976), have been modified to reflect both the current
allowable stress design and strength design philosophy. The MSJC-08 Code [4.3] does not
provide any guidance for any analysis or design approach. These examples present the ASD
approach for design of wall beams.

Example 4.28 Design of a single-span deep beam: allowable stress
design.
A nominal 8 in wide and 24 ft deep concrete masonry wall panel is supported over a
span (center-to-center of supports) 24 ft. The length of supports is 2 ft each as shown in
2
Fig. E4.28. The wall panel is fully grouted and weighs 100 lb/ft . The wall panel carries
a uniform load of 2500 lb/ft including its own weight. Calculate (a) the load-carrying
capacity of the wall panel and check if the panel can safely support its weight, (b) flex-
ural reinforcement requirements, and (c) shear reinforcement requirements. Use ′ f =
m
2
1500 lb/in. and Grade 60 reinforcement.
* These examples (based on ASD) are taken from Ref. 4.18 with permission from National Concrete Masonry
Association, Herndon, VA., and have been expanded by the author to reflect the provisions of both the allowable stress
design and strength design philosophy of MSJC-08 Code [4.3].